While anti-tuberculosis drugs can kill the culprit Mycobacterium tuberculosis (TB) bacilli in vitro, axenic culture in a few days, treatment of an infected human host takes on the order of 6 months. Treating clinically latent forms of TB requires even longer periods of time, ~ 9 months. The difference between the in vitro and in vivo requirement is thought to be due to TB bacilli existing in a different physiologic state in vivo that is potentially "drug tolerant" due to the assumption of a metabolically dormant, non-replicating state (1). Understanding what functions are essential in these dormant bacilli and the mechanisms by which they switch between non-replicating and replicating states would be invaluable to the development of more effective, potentially shorter course TB therapy. Because of the current limitations in TB genetics resulting in the inadequate ability to study essential gene functions, the identification and use of small molecule probes of the physiology of non-replicating bacteria will play an incredibly powerful role in the elucidation of this biology. The goal of this project is to develop potent, soluble small molecule probes that modulate survival of non-replicating TB bacilli, with good selectivity for TB over host cell types. These probes will be used to elucidate the physiology of non-replicating TB and to understand the functions that regulate the generation and maintenance of this state. PUBLIC HEALTH RELEVANCE: The World Health Organization has declared a global health emergency with the resurgence of tuberculosis in the setting of HIV infection and with the emergence of multi-drug resistant TB. Current TB drugs that were developed in the 1950-1960's are suboptimal because of their inadequate activity (including total lack of activity in drug resistant cases), toxicity, and the long course of therapy that is required to treat TB infection. Treatment length greatly hinders effective TB control due to the challenges of compliance, which contribute to the development of multi-drug resistance. New agents that achieve more rapid cures would transform the current pandemic;however, major barriers exist to developing such novel therapeutics including the lack of understanding of the in vivo physiologic states of TB bacilli as they adapt to the host microenvironment in order to survive for extended periods of time. We propose to address this problem through the development of small molecule probes which will be used to elucidate this physiology.